Characterizing Physicochemical Evolution of Biomass Particles during Fast Pyrolysis Using High-Resolution Simulation

快速热解是将废弃生物质转化为可燃气体和液体的一项重要技术；热解也发生在固体燃料燃烧的早期阶段。快速热解衍生的液体燃料被认为是一种经济上可行的化石燃料替代品，近年来一些热能和发电设施已经上线。然而，尽管快速热解具有广阔的发展前景，但生物质热解反应器条件的复杂性阻碍了快速热解的发展，而且到目前为止，还没有能够预测详细过程的方法。本项目的目标是通过高保真的数值模拟，准确地描述生物质颗粒的行为，并预测快速热解反应器的产物产率。拟议的研究活动将促进生物质热解用于能源应用的基础科学的进步。教育活动是为了让K-12科学教师参与研究，以促进关于可再生能源的教育。在美国，相当数量的K-12科学教师没有主修物理科学。对K-12科学教师的研究培训可以丰富他们的批判性思维，使他们能够将新知识融入课堂教学。拟议的研究计划是对生物质快速热解进行高分辨率模拟，并推导出用于工程CFD程序的子模型。将格子Boltzmann方法、离散元方法、化学动力学和颗粒收缩模型相结合，将一种新的模拟方法用于描述生物质颗粒的物理化学演化。计算结果将通过实验数据进行验证。在模拟结果的基础上，建立了阻力系数模型，并进行了检验。这项工作将解决几个对生物质热解至关重要的科学问题：颗粒的物理化学变化，颗粒-颗粒和气-颗粒相互作用，以及颗粒性质和操作条件对热解产物的影响。设计和优化高效生物质反应堆的根本困难在于缺乏对现实条件下颗粒行为的基本了解。这项研究将描述颗粒内的传输，小于颗粒尺寸的流场，化学反应，以及颗粒尺寸和性质的演变。科学界可以使用开源代码作为基础工具，进一步对固体颗粒的热解进行高级数值研究，例如煤炭、木屑、城市固体废物或聚合物材料。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Fast pyrolysis is a prominent technology in converting waste biomass to combustible gases and liquids; pyrolysis also occurs at the early stage of solid fuel combustion. Fast pyrolysis-derived liquid fuels are regarded as an economically feasible alternative to fossil fuels and some facilities for heat and power generation have been brought online in recent years. However, despite its promising potential, the development of fast pyrolysis has been hindered by the complexity of reactor conditions in biomass pyrolysis, and to date, methods capable of predicting the detailed processes are unavailable. The objectives of this project are to characterize accurately the behaviors of biomass particles and predict the product yields of a fast pyrolysis reactor by using high-fidelity numerical simulations. The proposed research activities will lead to advances in the fundamental science of biomass pyrolysis for energy applications. The educational activities are to engage K-12 science teachers in research in order to promote education on renewable energy. In the U.S., a significant number of K-12 science teachers have not majored in the physical sciences. The research training of K-12 science teachers can enrich their critical thinking and enable them to incorporate their new knowledge into their classroom teaching.The proposed research plan is to conduct high-resolution simulations of biomass fast pyrolysis and to derive submodels for use in engineering CFD codes. A novel simulation approach, one that combines the lattice Boltzmann method, discrete element method, chemical kinetics, and particle shrinkage modeling, will be employed to describe the physicochemical evolution of biomass particles. Computational results will be validated by experimental data. Based on the simulation results, a drag coefficient model will be derived and tested. This work will address several scientific topics of paramount importance to biomass pyrolysis: physicochemical changes of particles, particle-particle and gas-particle interactions, and effects of particle properties and operating conditions on the pyrolysis products. The underlying difficulty of designing and optimizing an efficient biomass reactor is the lack of fundamental understanding of particle behaviors under realistic conditions. This research will characterize intra-particle transport, flow fields smaller than particle size, chemical reactions, and evolutions of particle size and properties. The resulting open-source code can be used by the scientific community as a baseline tool for further advanced numerical study on the pyrolysis of solid particles, e.g., coal, wood chips, municipal solid waste, or polymer materials.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.